A. Field of Invention
This invention pertains to an apparatus constructed and arranged to operate in conjunction with a cardiomyoplastic muscle used to assist a heart, and more particularly, to an apparatus arranged and constructed to provide cardiac assist using the cardiomyoplastic muscle immediately after mobilization. Moreover, the apparatus is further used to train the muscle quickly and efficiently.
B. Description of the prior art
Severe chronic cardiac insufficiency arising from cardiac disease or injury shortens and degrades the quality of life of many patients. One form of severe chronic cardiac insufficiency, congestive heart failure, is a pathophysiological state in which cardiac output is inadequate to meet physiological requirements of the body. The mortality rate for congestive heart failure is greater than 50% within five years of onset. Treatments for severe chronic cardiac insufficiency include heart transplants, artificial heart implants and cardiomyoplasty. Cardiac transplantation, using cyclosporine to inhibit tissue rejection, is a very successful technique for prolonging a cardiac patient's life, improving the survival rate to 80% after one year. However, the transplant operation is very expensive and heart availability is limited. The artificial heart approach has had limited success to date.
Dynamic cardiomyoplasty is a surgical and electrical therapeutic technique used to overcome or at least alleviate cardiac insufficiency. This technique consists of using a skeletal muscle which is dissected from a patient, while maintaining its neural tissues and neurovascular structures, and is surgically placed around the patient's heart. An electrical stimulation device, with an electrical pulse generator and intramuscular electrodes, is implanted for performing muscle electrical stimulation in synchrony with ventricular systole to support cardiac pumping.
The skeletal muscles have been considered for use to augment myocardial performance in patients with dilated or ischemic cardiomyopathy. In cardiomyoplasty, the latissimus dorsi muscle (LDM) is wrapped around the heart and stimulated to contract in synchronization with the heart (in systole). In aortomyoplasty, the LDM is wrapped around the aorta and is stimulated to contract in cardiac diastole (counterpulsation). There are also other manifestations of counter pulsation. For example, in skeletal muscle ventricle (SMV), the LDM is wrapped around a small diameter cylinder or cone. The muscle pump is then connected to the circulation in such a way that it may be stimulated to contract during diastole to augment the diastolic blood pressure.
Presently, cardiomyoplasty patients suffering from ventricular fibrillation are treated by one of several methods, depending on the circumstances at the time of the onset of fibrillation. Ventricular fibrillation occurring in the hospital must be first confirmed by doctors or paramedical personnel. Standard high energy defibrillation shocks are then applied to the patient. Of course, these shocks must be applied by people having special training. If the ventricular fibrillation occurs outside a hospital, the patient must wait for trained medical help to arrive and apply the high energy shocks as discussed above.
Commonly assigned U.S. Pat. No. 5,251,621, incorporated herein by reference, proposes a therapy for preventing and terminating cardiac arrhythmias which may lead to ventricular fibrillation and sudden death in patients suffering from congestive heart failure. The proposed therapy combines antiarrhythmic pacing of various forms with skeletal muscle stimulation. Muscle stimulation increases cardiac output, aortic pressure and, therefore, perfusion of the heart to alleviate myocardial ischemia and ameliorate arrhythmias. A device performing pacing, defibrillation and skeletal muscle stimulation is disclosed in U.S. Pat. No. 5,251,621. However, this patent only teaches the stimulation of the skeletal muscle in synchronism with arrhythmia pacing in order to increase cardiac output.
Commonly assigned U.S. Pat. Nos. 4,796,630; 5,178,140; and 5,215,083 disclose devices performing both pacing and defibrillating functions. None of these references disclose, or even suggest, a device capable of performing defibrillation therapy which includes the stimulation of the skeletal muscle as part of the therapy.
In all applications, the stimulation is achieved by electrical pulses applied to the muscle via a pair of intramuscular leads, or a nerve electrode connected to a stimulator.
The latissimus dorsi, being skeletal muscle, is quickly fatigued under normal circumstances. However, repeated stimulation of the skeletal muscle transforms it into a fatigue-resistant muscle suitable for chronic ventricular assistance, enabling dynamic cardiomyoplasty. More specifically, sequential and progressive electrical stimulation of the muscle causes the glycolytic muscle fibers predominant in skeletal muscle to take the form of oxidative fibers. Oxidative fibers are resistant to fatigue and have histochemical and biochemical characteristics similar to the myocardium. The skeletal muscle thus treated is then trained to function so as to assist cardiac muscle to increase the patient's cardiac output.
In a standard application, the muscle tends to be ischemic after mobilization. As a result, electrical stimulation is usually not applied in the first two weeks after mobilization to prevent muscle necrosis. Furthermore, it was found that the original skeletal muscle is prone to fatigue, therefore for the muscle to work continuously, the muscle must be trained and transformed into fatigue resistant. The skeletal muscle can be transformed by low frequency electrical stimulation over a period of about 8 weeks with increasing regularity.
Therefore for about ten weeks after the procedure, the patients will not receive any significant hemodynamic benefits. Coupled with the fact that the patients' condition deteriorate because of the severity of the procedure, this may partially account for the perioperative mortality associated with cardiomyoplasty.